I think a pendant type metal halide light is good for a hex tank. A hex tank is not an easy one to light with fluorescent bulbs due to its shape. I would consider a 14K to 20K metal halide bulb for a hex tank.
If you are set for keeping just fish and soft corals only, you can use a low wattage one. However, a lot of people tend to migrate toward more light demanding corals as they get more familiar with the hobby. A lot of softies such as zoanthids and leathers actually love high light, and IMHO they look prettier under a metal halide light. If your budget allows, a 150W clip on type or pendant metal halide lamp would be really nice.
As for the must have's, a good skimmer is indispensable. A refugium is not easy to install on a hex tank unless you can make a hex shaped sump like 8Ball did for his. A remote system may work if you have a convenient place/method to hide it.
Tomoko